Dehydrocyclization of hydrocarbons

ABSTRACT

Process of dehydrocyclizing C6-C10 hydrocarbons having at least a C6 backbone using a Li, Na or K zeolite X or Y impregnated or ion exchanged with 0.1 to 1.2 weight percent Pt and impregnated or ion exchanged with 0.01 to 1.0 weight percent Cd at from 500 to 560 and preferably 510* to 555*C. using a partial pressure of hydrogen of from 10 to 300 p.s.i. and preferably 40 to 200 p.s.i. to form benzene and alkylbenzene.

[451 Aug. 27, 1974 DEHYDROCYCLIZATION OF HYDROCARBONS [75] Inventor: Masayoshi Oishi, Wilmington, Del.

[73] Assignee: Sun Research and Development Co.,

Philadelphia, Pa.

22 Filed: Dec.11, 1972 21 App1.No.:314,207

[52] US. Cl. 260/6735, 208/ 138 [51] Int. Cl. C07c 3/02, C07c 3/09 [58] Field of Search 260/673.5, 673; 208/138 [56] References Cited UNITED STATES PATENTS 2,971,903 2/1961 Kimberlin, Jr. et al 208/119 2,971,904 2/1961 Gladrow et al. 260/673 3,499,836 3/1970 Hayes et a1. 208/130 3,662,018

5/1972 Parker et a1. 260/683.3

3,663,430 5/1972 Morris 208/111 3,775,501 11/1973 Kaeding et al 3,775,502 11/1973 Oishi 260/673 Primary Examiner-Delbert E. Gantz Assistant Examiner.luanita M. Nelson Attorney, Agent, or Firm-Mr. George L. Church; Mr. J. Edward Hess; Mr. Frank C. Hilberg ABSTRACT Process of dehydrocyclizing C ,C hydrocarbons having at least a C backbone using a Li, Na or K zeolite X or Y impregnated or ion exchanged with 0.1 to 1.2 weight percent Pt and impregnated or ion exchanged with 0.01 to 1.0 weight percent Cd at from 500 to 560 and preferably 510 to 555C. using a partial pressure of hydrogen of from 10 to 300 p.s.i. and preferably 40 to 200 p.s.i. to form benzene and alkylbenzene.

7 Claims, N0 Drawings DEI-IYDROCYCLIZATION OF HYDROC H BACKGROUND OF THE INVENTION In the processing of petroleum into gasoline it is known to remove the normal paraffins from the gasoline due to their very low octane ratings. This operation is conveniently carried out with a molecular sieve absorbant. The normal hydrocarbons thus removed are then processed into more valuable products. One of these processes is reforming the normal paraffins into higher octane gasoline components. In reforming the normal paraffins are isomerized into isoparaffins, dehydrocyclized into aromatics and cracked into lower molecular weight paraffins and olefins. The process of the present invention is directed to maximizing the dehydrocyclizing of the normal paraffins into aromatics.

DESCRIPTION OF THE INVENTION The present invention relates to the dehydrocyclization of paraffins containing from six to carbon atoms to form aromatic compounds.

The catalyst used in the present invention is the lithium, sodium or potassium form of zeolite X or zeolite Y which has been impregnated or ion exchanged with platinum and cadmium. These zeolites are similar in cell size, density, void volume and aperture size. Sodium zeolite X has the typical formula:

Sodium zeolite Y has the typical formula:

Na55[ SIO2)13 A further description of these zeolites may be found in Crystalline Molecular Sieves by D. W. Breck, J. of CHEM. ED., 41, 678-689, (1964). For use in the present invention the exchangeable metal ions portion of the zeolite should be lithium, sodium or potassium. Thus either lithium or potassium may be substituted for part or all of the sodium in the normal synthetic zeolite. These substitutions are well known in the art and generally involve treating the zeolite with an aqueous solution of a salt of the metal which it is desired to substitute on the zeolite.

After the desired zeolite is obtained it is impregnated or ion exchanged with from 0.1 to 1.2 wt. percent as based on the zeolite of platinum. Below about 0.1 wt. percent platinum the catalyst is not sufficiently active. Above about 1.2 wt. percent platinum insufficient improvement in catalyst activity is obtained to warrant the use of more expensive platinum. The zeolite is readily impregnated with platinum by treatment with aqueous chloroplatinic acid at a moderately elevated temperature. In the preferred mode of the invention the platinum is ion exchanged onto the zeolite. This is readily accomplished by treatmentof the zeolite with an aqueous solution of both a lithium, sodium or potassium salt of a strong acid and a soluble platinum salt at a moderate temperature for several hours. Generally this treatment is carried out at from 25 to 80C. for a period of from 1 to 24 hours. The ion exchanged solution generally will contain from l X 10 to 0.1 molar platinumand from 1 to 10 molar sodium. The pH of the ion exchanged solution ordinarily will be from 7 to 9. The catalyst is then washed thoroughly with a solvent such as water to remove the salt residue and is then dried and ground. The catalyst is then calcined by heating at from 400 to 650C. in an oxygen-containing atmosphere such as air or pure oxygen for from 1 to 6 hours. The platinum is reduced to the free metal by treatment with flowing hydrogen for 1 to 4 hours at 350 to 550C. The catalyst is then treated with an aqueous solution of a soluble cadmium salt, the anionic portion of which can be volatilized away by heating. Generally only enough water need be present to wet the surface of the zeolite. Generally from 0.1 to 1.2 wt. percent as based onthe zeolite of cadmium is used. This treatment is normally done at a moderate temperature of from about 25 to C. for from 10 minutes to 4 hours. The catalyst is then dried by heating at to 200C. for from 1 to 24 hours. The catalyst is then calcined by heating at from 400 to 650C. in an oxygen containing atmosphere such as air or pure oxygen for from 1 to 6 hours. The platinum and cadmium are then reduced to the free metal by treatment with flowing hydrogen for 1 to 4 hours at 350 to 550C. This reduction results in the zeolite containing I-l zeolite sites. If desired these 11* zeolite sites can be converted back to alkali metal sites. This is readily done by treatment with 0.1 to 1 N sodium bicarbonate or its equivalent for 1 to 24 hours at 25-80C. followed by drying the catalyst.

The dehydrocyclization is generally carried out using a liquid hourly space velocity as based on feed of from 0.1 to 40 and preferably from 2 to 15. The dehydrocyclization is carried out at from 500 to 560C. and preferably 510 to 555C. Above 555C. and especially above 560C. the amount of cracking taking place starts to increase rapidly. Below about 500C. the amount of conversion of the paraffin is too low. The amount of cyclization as opposed to the amount of isomerization increases considerably at about 510C.

The dehydrocyclization is carried out under moderate-pressure expressed herein in terms of partial pressure of hydrogen in the reactor. The partial pressure of hydrogen generally is from 10 to 300 p.s.i.g. with from 50 to 200 p.s.i.g. being the preferred range. Below 50 p.s.i.g. and especially below 10 p.s.i.g. coking of the catalyst becomes too rapid to be economical. As the pressure increases above 200 p.s.i.g. and especially above 300 p.s.i.g. the cracking and isomerization reactions become favored instead of the dehydrocyclization reaction.

Suitable paraffinic starting materials contain from six to 10 carbon atoms. Generally, the normal paraffins are preferred because due to their low octane numbers, they can be improved more than the branched paraffins which have higher octane numbers. Ordinarily the feed stream will be the normal hydrocarbons removed by denormalization of a C -C petroleum stream which would of course consist essentially of C C normal hydrocarbons.

The present invention provides for a high selectivity of the converted material to cyclic hydrocarbons generally in excess of 70 wt. percent as based on starting material converted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A large quantity such as 100 g. of sodium zeolite X is air dried in an oven overnight at l 10C. A ten gram sample of the dried zeolite X is added to a flask containing 200 ml. of distilled water and 61.4 g. of NaCl. This mixture is stirred for 15 minutes while the temperature is maintained at 60C. A solution of 0.2 g. of

through the septum and the resultant effluent is programmed through a previously calibrated gas chromatograph. The definitions of selectivity reported in the table are:

cake-like catalyst is washed thoroughly until it is subcyclizmion y aromatics p stantially free of chlorine. The catalyst is dried for 2 mews/Conversion X 100 hours at 100C i an Oven f hi i i h d ground 7? isomerization (lsom) total isomers of 7 carbon until it passes through a No. 40 mesh screen (U.S. Sieve atoms 7! )/C0I1Vf$i0h X loo Series). The catalyst is then calcined at 500C. with C a g total of 6 and lower Carbon cc./min. of air flowing. The final temperature is 0 atoms (wt. %)/conversion (wt. X 100 reached in about 2 hours. This catalyst is used in Runs It is apparent from an inspection of the table that l and 3 in which runs the catalyst is reduced with hy- Runs 2 and 4 which use the cadmium doped catalyst drogen in the reactor at 500C. before the runs. are clearly superior in achieving the desired result.

TABLE Temp. H. Press. Conversion Selcctivitv Run C. psig. ycl lsom Cruel; Cycl/Cmck 1 500 50 45.3 46.4 3x11 250 1.x1 2 500 59 52.5 70.4 14.9 14.7 4.79 3 520 50 we, (10.5 1-1.: 25.3 .59 4 520 50 87.7 7&5 7.3 14.5 5.411

An additional portion of the catalyst is prepared in The invention claimed is: the same way as described above through the calcining l. A process of dehydrocyclizing at least one normal step. The catalyst is then reduced with flowing hydroparaffi containing from six to 10 carbon atoms comgen for 2 hours at 500C. Three tenths of 1 percent as prising contacting said normal paraffin with a catalyst based on the catalyst of cadmium in the form of which is zeolite selected from the class consisting of zea)2' 2 was mixed with the Catalyst and a olite X and zeolite Y which zeolite contains from 0.1 small amount of water is added to wet the mixture. The to 1 2 i h percent as b d o s id zeolite of platiteshhihg slurry is hand mixed thoroughly for thirty num and from 0.1 to 1.2 weight percent as based on Utes and dried in an Oven at 1 overhight- The said zeolite of cadmium in the free metal state, the acid alyst is then calcined at 500C. with 10 cc./min. of air Sites f id li b i fill d i h Hfl Li N or howihg- The hhai temperature is reached in about 2 ions or mixtures thereof at from 500C. to 560C, at :1 hours. This catalyst is used in Runs 2 and 4 in which li id h l Space l i f f 1 to under 3 runs the catalyst is reduced with hydrogen in the reachydrogen partial pressure f f 10 to 300 i tor at 500C. before the runs. In Runs 1 to 4 a pulse miwhereby at least a portion f i normal ff i croreactor is used. This reactor is a stainless steel tube dehydi-OcydiZed about 200 mm. long and having an inside diameter of 2 The process f Claim 1 wherein the platinum has 4 The inside of the tube Contains Py WOO] 40 been ion exchanged onto the zeolite and then reduced tainers which keep the catalyst in place. In each of the to the f meta] Siam runs the tube is Packed with 0-i25 of catalyst- The 3. The process of claim 2 wherein the zeolite is zeotube is fitted in a brass mounting sleeve which contains m a thermocouple in a well. The brass sleeve in turn is 4 The process f ciaim 3 wherein the hydrogen mounted in a 4-inch electric furnace operated on 115 tiai pressure is f about i0 200 VOltS and Controlled y a p Powersmh The top 5. The process of claim 4 wherein the temperature is of the tube is fitted with a silicone rubber septum from 5 to 555 mounted in a septum holder and a carrier gas inlet. The 6. The process of claim 5 wherein the feed quid carrier gas is deoxygenated dry hydrogen passed hourly Space velocity is from 2 f 15' through the system at a rate of about 50 cc. per minute 50 7. The process of claim 6 wherein the paraffin start- Uhdet the Pressure ihdiftated P i h heihg ing material is a hydrocarbon feed stream consisting esreported- The Catalyst precohdmohediby ihlectmg a sentially of normal paraffins containing from six to 10 30 microliter pulse of the n-heptane which 15 the nor- Carbon atoms. mal paraffin being dehydrocyclized in all of the runs. The reactor effluent from this pulse is not analyzed. A 2 microliter charge of the n-heptane is then injected 

2. The process of claim 1 wherein the platinum has been ion exchanged onto the zeolite and then reduced to the free metal state.
 3. The process of claim 2 wherein the zeolite is zeolite X.
 4. The process of claim 3 wherein the hydrogen partial pressure is from about 50 p.s.i.g. to 200 p.s.i.g.
 5. The process of claim 4 wherein the temperature is from 510*C. to 555*C.
 6. The process of claim 5 wherein the feed liquid hourly space velocity is from 2 to
 15. 7. The process of claim 6 wherein the paraffin starting material is a hydrocarbon feed stream consisting essentially of normal paraffins containing from six to 10 carbon atoms. 